The present invention relates to new polymeric materials, especially suitable for use in biomedical applications, processes for their production, articles formed from such materials and processes for modifying the physical and biological properties of plastic materials. The medical device industry frequently employs a range of thermoplastic, elastomeric and thermoset materials in medical devices. Many of these polymers were originally developed as engineering materials and their physical and mechanical properties reflect this. Thus a plastic may be employed as a medical device because it posseses physical and mechanical properties suitable for use in a biological environment. However, until recently little attention was paid to the biological properties of these materials. This has resulted in a number of problems with current device materials as a result of adverse biological reactions. Silicone rubbers have been shown to leach toxic silicones when implanted, polyurethanes have been found to degrade by macrophage attack and natural rubbers have caused severe allergic reactions. In addition, PVC, a widely used polymer for medical devices, often contains large quantities of the plasticiser bis-(2-ethylhexyl)phthalate and many studies now show this to be toxic. It is clear, therefore, that many materials possess properties which render them unsuitable for use in biological applications.
Previous attempts to prepare biocompatible materials have mimicked the surface of platelet cells which under normal circumstances exist in the blood without causing any adverse reactions. These cell membranes comprise a phospholipid bilayer with the phosphorylcholine group dominating the external membrane surface. It is believed this outer surface avoids adverse reaction with other biological components. Lipids containing phosphorylcholine groups have been coated on to the surface of device materials and bloodclotting studies showed that they rendered the surface more biocompatible (J A Hayward and D Chapman, Biomaterials, Vol. 5, 135, 1984). These phospholipids have also been used as plasticisers in commercial polymers and have again improved the biocompatibility of the base material (WO-A-87/02684). However these two approaches nevertheless possess disadvantages.
Coating the surface of a finished device has a number of problems, one being the difficulty in coating devices with complex shapes or multiple components; in practice a multi-component device can be impossible to coat. In addition the degree of biocompatibility is dependent on the quality of the coating and how strongly it is bound to the surface; thus defects or scratches in the coating will reduce its effectiveness. The use of a lipid as a plasticiser goes some way to overcome these problems, but the lipid is free to move through the material and can eventually leach out of the system. This can again lead to a reduction in the level of biocompatibility. The lipid also has in addition no mechanical strength and can therefore only be used to soften the base polymer.
We have now devised new blended polymeric materials which seek to overcome these disadvantages. The blends combine the desirable physical and/or mechanical properties of an engineering polymer with the biocompatible properties of a polymer bearing pendant zwitterionic, for example phosphoryl choline, groups.
The present invention accordingly provides a polymer blend comprising:
(A) a polymer bearing zwitterionic pendant groups; and
(B) a polymer having desirable mechanical and/or physical properties.
The extent to which a polymer bearing zwitterionic pendant groups (A) renders a further polymer biocompatible in a blend may be assessed as a combination of factors such as reduction in the extent to which the blend causes blood platelet activation and protein adsorption, (for instance as judged by absorption of fibrinogen from human plasma).
The polymer bearing zwitterionic pendant groups may be either a homopolymer or a copolymer. Preferably it is a polymer of residues of one or more radically polymerisable monomers, more preferably ethylenically unsaturated monomers. Preferably the polymer bears zwitterionic pendant groups by virtue of one of the starting monomers from which it is produced carrying such a group. Instead the zwitterionic group may be introduced onto a preformed polymer, for instance by reactions such as are disclosed in EP-A-0157469, WO-A-9113639, WO-A-9207858 or WO-A-9305081. The polymer may be a condensation polymer, for instance a polyurethane or a polyester. Again the zwitterionic group is present on the polymer either by incorporation as a pendant group on one of the starting monomers or by post-reaction of a preformed polymer. Polyurethanes are described in WO-A-8602933 and WO-A-89305081 and polyesters and described in WO-8800956.
Preferably the zwitterionic group is a group X as defined below.
Preferably the polymer is a copolymer of a comonomer containing a zwitterionic group and a comonomer containing an alkyl, usually a hydrophobic group, a reactive functional group, or an ionic group. The presence of residues of such comonomers may serve to improve the compatability of the polymer (A) for the polymer (B) in the blend of the present invention. Copolymers containing residues of a comonomer which contain a hydrophobic group are particularly preferred.
As examples of comonomers containing as hydrophobic groups, mention may be made of comonomers containing as pendant groups alkyl groups or fluoroalkyl groups, optionally having one or more etheric oxygen atoms interrupting the carbon chain, and optionally containing one or more carbon-carbon double or triple ones. Alternatively such comonomers may contain as pendant groups siloxane groups, preferably containing from 1 to 50, more preferably 5 to 30, silicon atoms.
The nature of such hydrophobic groups may be chosen for comparability with polymer (B). For example comonomers containing a hydrophobic fluoroalkyl group are particularly suitable for blending with fluoropolymer such as polyvinylidene fluoride (PVDF).
Alternatively, the polymer may comprise residues of a monomer containing both a zwitterionic group and such a hydrophobic group.
Preferably, such a hydrophobic group is an alkyl or fluoroalkyl group, optionally containing one or more carbon-carbon double or triple bonds. More preferably, the hydrophobic group does not contain any ethylenic unsaturation.
Alternatively, or in addition, such copolymers may further comprise residues of a comonomer containing a reactive functional group or an ionic group. Such reactive groups may serve to crosslink the copolymer (A) and/or bind the copolymer (A) to the polymer (B) having desirable physical and/or mechanical properties. In addition such reactive groups may provide reactive moieties at the surface of the blend. Use of a comonomer of containing ionic groups may serve to improve the miscability of the polymer (A) with polymer (B) where polymer (B) itself bears ionically charged groups.
In addition, the polymer (A) may further comprise residues of one or more diluent comonomers.
Monomers and comonomers of ethylenically unsaturated monomers which may be used in the preferred polymers (A) will now be described in more detail.
It is to be understood that throughout the specification (alk)acrylate, (alk)acrylic and (alk)acrylamide mean acrylate or alkacrylate, acrylic or alkacrylic and acrylamide or alkacrylamide respectively.
Preferably unless otherwise stated alkacrylate, alkacrylic and alkacrylamide groups contain from 1 to 4 carbon atoms in the alkyl group thereof and are most preferably methacrylate, methacrylic or methacrylamide groups. Similarly (meth)acrylate, (meth)acrylic and (meth)acrylamide shall be understood to mean acrylate or methacrylate, acrylic or methacrylic and acrylamide or methacrylamide respectively.
A.1. Monomers Containing a Zwitterionic Group
Preferred comonomers which contain a zwitterionic group are of general formula (I)
Yxe2x80x94Bxe2x80x94Xxe2x80x83xe2x80x83(I)
wherein B is a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene chain optionally containing one or more fluorine atoms up to and including perfluorinated chains or, if X contains a carbon-carbon chain between B and the zwitterionic moiety or if Y contains a terminal carbon atom bonded to B, a valence bond;
X is a zwitterionic group and
Y is an ethylenically unsaturated polymerisable group selected from 
wherein:
R is hydrogen or a C1-C4 alkyl group;
A is xe2x80x94Oxe2x80x94 or xe2x80x94NR1xe2x80x94 where R1 is hydrogen or a C1-C4 alkyl group or R1 is xe2x80x94Bxe2x80x94X where B and X are as defined above; and
K is a group xe2x80x94(CH2)pOC(O)xe2x80x94, xe2x80x94(CH2)pC(O)Oxe2x80x94, xe2x80x94(CH2)pOC(O)Oxe2x80x94, xe2x80x94(CH2)pNR2xe2x80x94, xe2x80x94(CH2)pNR2C(O)xe2x80x94, xe2x80x94(CH2)pC(O)NR2xe2x80x94, xe2x80x94(CH2)pNR2C(O)Oxe2x80x94, xe2x80x94(CH2)pOC(O)NR2xe2x80x94, xe2x80x94(CH2)pNR2(O)NR2xe2x80x94, (in which the groups R2 are the same or different) xe2x80x94(CH2)pOxe2x80x94, xe2x80x94(CH2)pSO3xe2x80x94, or, optionally in combination with B, a valence bond and p is from 1 to 12 and R2 is hydrogen or a C1-C4 alkyl group.
The proviso on whether B may be a valence bond ensures that the zwitterionic moiety in X is not directly bonded to a heteroatom, such as an oxygen or nitrogen atom in Y.
Preferred monomers containing a zwitterionic group are therefore of general formula (II) or (III). 
where R, A, B, K and X are as defined with reference to formula (I).
Preferably in the compounds of formula (II) R is hydrogen, methyl, or ethyl, more preferably methyl, so that (II) is an acrylic acid, methacrylic acid or ethacrylic acid derivative.
In the compounds of formula (III) K may be a valence bond and B a group, K may be a group and B a valence bond, both K and B may be groups, or K and B may together be a valence bond. Preferably B is a group where K is a valence bond.
Where K is a group then preferably p is from 1 to 6, more preferably 1,2 or 3 and most preferably p is 1. When K is a group xe2x80x94(CH2)pNR2xe2x80x94, xe2x80x94(CH2)pNR2C(O)xe2x80x94, xe2x80x94(CH2)pC(O)NR2, xe2x80x94(CH2)pNR2C(O)Oxe2x80x94, xe2x80x94(CH2)pOC(O)NR2xe2x80x94 or xe2x80x94(CH2)pNR2C(O)NR2xe2x80x94 then R2 is preferably hydrogen, methyl or ethyl, more preferably hydrogen.
In the compounds of formula (III) preferably the vinyl group is para to the group xe2x80x94Kxe2x80x94Bxe2x80x94X.
Preferably B is:
an alkylene group of formula xe2x80x94(CR32)axe2x80x94, wherein the groups xe2x80x94(CR32)xe2x80x94 are the same or different, and in each group xe2x80x94(CR)32)xe2x80x94 the groups R3 are the same or different and each group R3 is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl, preferably hydrogen, and a is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety, more preferably xe2x80x94CH2O(CH2)4xe2x80x94; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR42)bO]c(CR42)bxe2x80x94 where the groups xe2x80x94(CR42)xe2x80x94 are the same or different and in each group xe2x80x94(CR42)xe2x80x94 the groups R4 are the same or different and each group R4 is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl, preferably hydrogen, and b is from 1 to 6, preferably 2 or 3 and c is from 2 to 11, preferably 2 to 5; or
if X contains a carbon-carbon chain between B and the centre of permanent positive charge or if Y contains a terminal carbon atom, a valence bond.
Preferred groups B include alkylene, oxaalkylene and oligo-oxaalkylene groups of up to 12 carbon atoms optionally containing one or more fluorine atoms.
In compounds of formula (III) it is preferred that K and B contain up to 12 carbon atoms in total.
Preferred zwitterionic groups for instance which are groups on ethylenically unsaturated monomer YBX are groups in which the cationic moiety is based on a quaternary ammonium group and the anionic moiety is based on a phosphate group. Preferred zwitterionic groups are ammonium phosphate ester zwitterionic groups. Usually the cationic is located aet the end of pendant group X distant from B. Most preferred are the groups of formula (IVA), (IVB), (IVC), (IVD) and (IVE) as defined below: monomers containing such groups may be used alone in homopolymers or in combination with further comonomers to provide a copolymer. Of these groups (IVB) are particularly preferred.
In addition, groups of formula (VA), (VB) and (VC) are preferred as monomers containing both a zwitterionic group and a hydrophobic alkyl, fluoroalkyl or siloxane group.
The groups of formula (IVA) are: 
where the groups R6 are the same or different and each is hydrogen or C1-4 alkyl and d is from 2 to 4.
Preferably the groups R6 are the same. It is also preferable that at least one of the groups R6 is methyl, and more preferable that the groups R6 are both methyl.
Preferably d is 2 or 3, more preferably 3.
When X is a group of formula (IVA) preferably B is a group of formula xe2x80x94(CR32)xe2x80x94 or xe2x80x94(CR32)2xe2x80x94, eg. xe2x80x94(CH2)xe2x80x94 or xe2x80x94(CH2CH2)xe2x80x94.
The groups of formula (IVB) are: 
where the groups R7 are the same or different and each is hydrogen or C1-4 alkyl, and e is from 1 to 4.
Preferably the groups R7 are the same. It is also preferable that at least one of the groups R7 is methyl, and more preferable that the groups R7 are all methyl.
Preferably e is 2 or 3, more preferably 2.
When X is a group of formula (IVB) preferably B is a group of formula xe2x80x94(CR32)xe2x80x94 or xe2x80x94(CR32)2xe2x80x94, eg. xe2x80x94(CH2)xe2x80x94 or xe2x80x94(CH2CH2)xe2x80x94.
The groups of formula (IVC) are: 
wherein the groups R8 are the same or different and each is hydrogen or C1-4 alkyl, R8a is hydrogen or, more preferably, a group xe2x80x94C(O)B1R8b where R8b is hydrogen or methyl, preferably methyl, B1 is a valence bond or straight or branched alkylene, oxaalkylene or oligo-oxaalkalyene group, and f is from 1 to 4; and
if B is other than a valence bond Z is 1 and if B is a valence bond Z is O, if X is directly bonded to an oxygen or nitrogen atom and otherwise Z is 1.
Preferably the groups R8 are the same. It is also preferable that at least one of the groups R8 is methyl, and more preferable that the groups R8 are all methyl.
Preferably f is 1 or 2, more preferably 2.
Preferably B1 is:
a valence bond;
an alkylene group of formula xe2x80x94(CR3a2)aaxe2x80x94, wherein the groups xe2x80x94(CR3a2)xe2x80x94 are the same or different, and in each group xe2x80x94(CR3a2)xe2x80x94 the groups R3a are the same or different and each group R3a is hydrogen or C1-4 alkyl, preferably hydrogen, and aa is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety, more preferably xe2x80x94CH2O(CH2)4xe2x80x94; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR4a2)baO]caxe2x80x94 where the groups xe2x80x94(CR4a2)xe2x80x94 are the same or different and in each group xe2x80x94(CR4a2)xe2x80x94 the groups R4a are the same or different and each group R4c is hydrogen or C1-4 alkyl, preferably hydrogen, and ba is from 1 to 6, preferably 2 or 3, and ca is from 1 to 12, preferably 1 to 6.
Preferred groups B1 include a valence bond and alkylene, oxaalkylene and oligo-oxaalkylene groups of up to 12 carbon atoms.
Preferably B and B1 are the same.
When X is a group of formula (IVC) preferably B is a group of formula xe2x80x94[(CR42CR42)cOb]CR42CR42xe2x80x94, eg. xe2x80x94(CH2CH2O)c(CH2CH2)xe2x80x94.
The groups of formula (IVD) are: 
wherein the groups R9 are the same or different and each is hydrogen or C1-C4 alkyl, R9a is a hydrogen or, more preferably, a group xe2x80x94C(O)B2R9b, R9b is hydrogen or methyl, preferably methyl, B2 is a valence bond or a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene group, and g is from 1 to 4; and
if B is other than a valence bond Z is 1 and if B is a valence bond Z is O if X is directly bonded to an oxygen or nitrogen atom and otherwise Z is 1.
Preferably the groups R9 are the same. It is also preferable that at least one of the groups R9 is methyl, and more preferable that the groups R9 are all methyl.
Preferably g is 1 or 2, more preferably 2.
Preferably B2 is:
a valence bond;
an alkylene group of formula xe2x80x94(CR3b2)abxe2x80x94, wherein the groups xe2x80x94(CR3b2)xe2x80x94 are the same or different, and in each group xe2x80x94(CR3b2)xe2x80x94 the groups R3b are the same of different and each group R3b is hydrogen or C1-4 alkyl, preferably hydrogen, and ab is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6, carbon atoms in each alkyl moiety, more preferably xe2x80x94CH2O(CH2)4xe2x80x94; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR4b2)bbO]cbxe2x80x94 where the groups xe2x80x94(CR4b2)xe2x80x94 are the same or different and in each group xe2x80x94(CR4b2)xe2x80x94 the groups R4b are the same or different and each group R4b is hydrogen or C1-4 alkyl, preferably hydrogen, and bb is from 1 to 6, preferably 2 or 3, and cb is from 1 to 12, preferably 1 to 6.
Preferred groups B2 include a valence bond and alkylene, oxalkylene and oligo-oxalkylene groups of up to 12 carbon atoms.
Preferably B and B2 are the same.
When X is a group of formula (IVD) preferably B is a group of formula xe2x80x94[(CR42CR42)bO]cCR42CR42xe2x80x94, eg. xe2x80x94(CH2CH2O)cCH2CH2xe2x80x94.
The groups of formula (IVE) are: 
wherein the groups R10 are the same or different and each is hydrogen or C1-4 alkyl, R10a is hydrogen or, more preferably, a group xe2x80x94C(O)B3R10b where R10b is hydrogen or methyl, preferably methyl, B3 is a valence bond or a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene group, and h is from 1 to 4; and
if B is other than a valence bond Z is 1 and if B is a valence bond Z is O if X is directly bonded to the oxygen or nitrogen and otherwise Z is 1.
Preferably the groups R10 are the same. It is also preferable that at least one of the groups R10 is methyl, and more preferable that the groups R10 are all methyl.
Preferably h is 1 or 2, more preferably 2.
Preferably B3 is:
a valence bond;
an alkylene group of formula xe2x80x94(CR3c2)acxe2x80x94, wherein the groups xe2x80x94(CR3c2)xe2x80x94 are the same or different, and in each group xe2x80x94(CR3c2)xe2x80x94 the groups R3c are the same or different and each group R3c is hydrogen or C1-4 alkyl, preferably hydrogen, and ac is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety, more preferably xe2x80x94CH2O(CH2)4xe2x80x94; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR4c2)bcO]ccxe2x80x94 where the groups xe2x80x94(CR4c2)xe2x80x94 are the same or different and in each group xe2x80x94(CR4c2)xe2x80x94 the groups R4c are the same or different and each group R4c is hydrogen or C1-4 alkyl, preferably hydrogen, and bc is from 1 to 6, preferably 2 or 3, and cc is from 1 to 12, preferably 1 to 6.
Preferred groups B3 include a valence bond and alkylene, oxaalkylene and oligo-oxaalkylene groups of up to 12 carbon atoms.
Preferably B and B3 are the same.
When X is a group of formula (IVE) preferably B is a group of formula xe2x80x94[(CR42CR42)bO]cCR42CR42xe2x80x94, eg. xe2x80x94(CH2CH2O)cCH2CH2xe2x80x94.
Further zwitterionic groups are of formula (VA), (VB) and (VC). These groups also contain an alkyl, fluoroalkyl or siloxane group. Monomers containing such a group are therefore particularly suitable for use in polymers without separate comomoners containing a hydrophobic group.
The groups of formula (VA) are: 
wherein the groups R11 are the same or different and each is hydrogen or C1-4 alkyl, R11a is either
(a) a group xe2x80x94[C(O)]vw (CR11b2)ww (SiR11c2) (OSiR11c2)vv R11c in which each group R11b is the same or different and is hydrogen or alkyl of 1 to 4 carbon atoms, each group R11c is the same or different and is alkyl of 1 to 4 carbon atoms or aralkyl, for example benzyl or phenethyl, vw is 0 or 1, ww is from 0 to 6 with the proviso that vw and ww are not both 0, and vv is from 0 to 49;
(b) a group of formula xe2x80x94C(O)B4xe2x80x94R11d, in which R11d is hydrogen or methyl, B4 is a valence bond or straight or branched alkylene, oxaalkylene or oligo-oxaalkalyene group optionally containing one or more fluorine atoms, and containing from 6 to 24, preferably 6 to 18 carbon atoms; i is from 1 to 4; and
if B is other than a valence bond Z is 1 and if B is a valence bond Z is 0 if X is directly bonded to an oxygen or nitrogen atom and otherwise Z is 1.
Preferably the groups R11 are the same. It is also preferable that at least one of the groups R11 is methyl, and more preferable that the groups R11 are all methyl.
Preferably i is 1 or 2, more preferably 2.
Where R11a is a siloxane group as defined in (a) above, each group (CR11b2) may be the same or different, preferably the same, and preferably each group R11b is hydrogen. Preferably ww is from 2 to 4, and is most preferably 3 when vw is 0 or 2 when vw is 1. Each group (SiR11c2) may be the same or different, preferably the same, and preferably each group R11c is methyl. Preferably vv is from 4 to 29.
Preferably the group R11a is a group xe2x80x94C(O)B4R11d as defined above. In such a case, preferably B4 is:
a valence bond;
an alkylene group of formula xe2x80x94(CR3d2)adxe2x80x94, wherein the
groups xe2x80x94(CR3d2)xe2x80x94 are the same or different, and in each group xe2x80x94(CR3d2)xe2x80x94 the groups R3d are the same or different and each group R2d is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl, preferably hydrogen or fluorine, and ad is from 1 to 24, preferably 6 to 18;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms -and optionally one or more fluorine atoms in each alkyl moiety, or
an oligo-oxalkylene group of formula xe2x80x94[(CR4d2)bdO]cdxe2x80x94 where the groups xe2x80x94(CR4d2)xe2x80x94 are the same or different and in each group xe2x80x94(CR4d2)xe2x80x94 the groups R4d are the same or different and each group R4d is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl, preferably hydrogen or fluorine, and bd is from 2 to 6, preferably 3 or 4, and cd is from 1 to 12, preferably 1 to 6.
In one embodiment B and B may be the same.
The groups of formula (VB) are: 
wherein the groups R12 are the same or different and each is hydrogen or C1-C4 alkyl, R12a is either
(a) a group xe2x80x94[C(O)]tu (CR12b2)uu (SiR12c2) (OSiR12c2)tt R12c in which each group R12b is the same or different and is hydrogen or alkyl of 1 to 4 carbon atoms, each group R12c is the same or different and is alkyl of 1 to 4 carbon atoms or aralkyl, for example benzyl or phenethyl, tu is 0 or 1, uu is from 0 to 6, with the proviso that tu and uu are not both 0, and tt is from 0 to 49; or
(b) a group of formula xe2x80x94C(O)B5xe2x80x94R12d, in which R12b is hydrogen or methyl, B5 is a valence bond or a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene group optionally containing one or more fluorine atoms and from 6 to 24 carbon atoms, more preferably 6 to 18 carbons atoms,
j is from 1 to 4; and
if B is other than a valence bond, Z is 1 and if B is a valence bond Z is 0 if X is directly bonded to an oxygen or nitrogen atom and otherwise Z is 1.
Preferably the groups R12 are the same. It is also preferable that at least one of the groups R12 is methyl, and more preferable that the groups R12 are all methyl.
Preferably j is 1 or 2, more preferably 2.
Where R12a is a siloxane group as defined in (a) above, each group (CR12b2) may be the same or different, preferably the same, and preferably each group R12b is hydrogen. Preferably uu is from 2 to 4, and is most preferably 3 when tu is 0 or 2 when tu is 1. Each group (SiR12c2) may be the same or different, preferably the same, and preferably each group R12c is methyl. Preferably tt is from 4 to 29.
Preferably the group R12a is a group xe2x80x94C(O)B4R12d as defined above. In such a case, preferably B5 is:
a valence bond;
an alkylene group of formula xe2x80x94(CR3e2)aexe2x80x94, wherein the groups xe2x80x94(CR3e2)xe2x80x94 are the same or different, and in each group xe2x80x94(CR3e2)xe2x80x94 the groups R3e are the same of different and each group R3e is hydrogen, fluorine or C1-4 alkyl, or fluoroalkyl, preferably hydrogen or fluorine, and ae is from 1 to 24, preferably 6 to 18;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms and optionally one or more fluorine atoms in each alkyl moiety; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR4e2)beO]cexe2x80x94 where the groups xe2x80x94(CR4e2)xe2x80x94 are the same or different and in each group xe2x80x94(CR4e2)xe2x80x94 the groups R4e are the same or different and each group R4e is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl, preferably hydrogen or fluorine, and be is from 2 to 6, preferably 3 or 4, and ce is from 1 to 12, preferably 1 to 6.
In one embodiment B and B5 may be the same.
The groups of formula (VC) are: 
where the groups R13 are the same or different and each is hydrogen or C1-4 alkyl, R13a is either
(a) a group xe2x80x94[C(O)]rs(CR13b2)ss (SiR13c2) (OSiR13c2)rr R13c in which each group R13b is the same or different and is hydrogen or alkyl of 1 to 4 carbon atoms, each group R13c is the same or different and is alkyl of 1 to 4 carbon atoms or aralkyl, for example benzyl or phenethyl, rs is 0 or 1, ss is from 0 to 6, with the proviso that rs and ss are not both 0, and rr is from 0 to 49; or
(b) a group of formula xe2x80x94C(O)B6xe2x80x94R13d, in which R13a is hydrogen or methyl, B6 is a valence bond or a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene group optionally containing one or more fluorine atoms and from 6 to 24, more preferably 6 to 18 carbon atoms and k is from 1 to 4; and
if B is other than a valence bond, Z is 1 and if B is a valence bond Z is 0 if X is directly bonded to an oxygen or nitrogen atom and otherwise Z is 1.
Preferably the groups R13 are the same. It is also preferable that at least one of the groups R13 is methyl, and more preferable that the groups R13 are all methyl.
Preferably k is 1 or 2, more preferably 2.
Where R13a is a siloxane group as defined in (a) above, each group (CR13b2) may be the same or different, preferably the same and preferably each group R13b is hydrogen. Preferably ss is from 2 to 4, and is most preferably 3 when rs is 0 or 2 when rs is 1. Each group (SiR13c2) may be the same, or different, preferably the same, and preferably each group R13c is methyl. Preferably rr is from 4 to 29.
Preferably the group R13a is a group xe2x80x94C(O)B6R13d as defined above. In such a case, preferably B6 is:
a valence bond;
an alkylene group of formula xe2x80x94(CR3f2)afxe2x80x94, wherein the groups xe2x80x94(CR3f2)xe2x80x94 are the same or different, and in each group xe2x80x94(CR3f2)xe2x80x94 the groups R3f are the same or different and each group R3f is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl, preferably hydrogen or fluorine, and is from 1 to 24, preferably 6 to 18;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms and optionally one or more fluorine atoms in each alkyl moiety; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR4f2)bfO]cfxe2x80x94 where the groups xe2x80x94(CR4f2)xe2x80x94 are the same or different and in each group xe2x80x94(CR4f2)xe2x80x94 the groups R4f are the same or different and each group R4f is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl, preferably hydrogen or fluorine, and bf is from 2 to 6, preferably 3 or 4, and cf is from 1 to 12, preferably 1 to 6.
In one embodiment B and B6 may be the same.
Particular examples of preferred monomers containing a zwitterionic group are 2-(methacryloyloxy)ethyl-2xe2x80x2-(trimethylammonium)ethyl phosphate inner salt and 1[4(4xe2x80x2-vinylbenzyloxy)butane]-2xe2x80x2(trimethylammonium)ethyl phosphate inner salt.
Monomers containing a zwitterionic group such as those of formula (II) and (III) may be prepared by conventional techniques using known reactions, for example using a suitable substituted alkyl (alk)acrylate or suitable substituted styrene as precursor. Examples of suitable substituted alkyl (alk)acrylates include dimethylaminoethyl(meth)acrylate and 2-hydroxyethyl(meth)acrylate.
Monomers of formula (II) or (III) containing a group of formula (IVA) or (IVB) may be prepared as described in the Reference Examples herein or by analogous known methods.
Monomers of formula (II) or (III) containing a group of formula (IVC) in which R8a is xe2x80x94C(O)B1R8b may be prepared by selective acylation of glycerophosphorylcholine or analogues thereof at the primary hydroxyl group with an activated acid derivative such as an acid anhydride O(C(O)B1R8b)2 or an acid halide R8bB1COHAl where B1 and R8b are as defined above and Hal is halogen, followed by acylation of the secondary hydroxyl group with an appropriate acylating agent, for example methacryloyl chloride. Purification, for example by column chromatography on a suitable support, may be performed after each acylation or after the second acylation only. Suitable activated acid derivatives include acid anhydrides, acid halides, reactive esters and imidazolides. The acylations may be performed in a suitable anhydrous, aprotic solvent, for example N,N-dimethylformamide, optionally in the presence of a suitable non-nucleophilic base, for example triethylamine.
Alternatively, the primary alcohol group in glycerophosphoryl choline or an analogue thereof may be blocked by reaction with a suitable protecting group reagent, for example t-butyldimethylsilyl chloride, under standard conditions and the secondary hydroxy group then treated with an acylating agent such as methacryloyl chloride. The t-butyldimethylsilyl protecting group may be removed by treatment with a dilute organic or mineral acid, for example p-toluene sulphonic acid, hydrochloric acid or with tetra-butylammonium fluoride. The deblocked primary hydroxyl group may then be treated with an activated acid derivative such as an acid anhydride O(C(O)B1R8b)2 or acid halide R8bB1COHal where B1 and R8b are as defined above, and Hal is halogen.
Analogues of glycerophosphorylcholine (compounds of formula (II) or (III) containing a group (IVD) where R8a is hydrogen) may be prepared by reaction of phosphorus oxychloride with a bromoalcohol in an inert aprotic solvent, such as dichloromethane, to give a bromoalkylphosphorodichloridate. The dichloro derivative thus produced may then be treated with an appropriately protected glycerol derivative, for example 2,2-dimethyl 1,3-dioxolane-4-methanol, in the presence of a base, for example triethylamine, followed by acid hydrolysis to give a bromoalkylphosphoro-glycerol derivative. This may then be treated with an amine NR83, where R8 is as defined above, for example trimethylamine, to generate the glycerophosphorylcholine analogue. This preparation is depicted in the following scheme. 
where R8 and f are as defined in relation to groups of formula (IVC).
Monomers of formula (II) or (III) containing a group of formula (IVD) in which R9a is xe2x80x94C(O)B2R9b may be prepared by the selective acylation of glycerophosphorylcholine or an analogue thereof at the primary hydroxyl group with for example, methacryloyl chloride followed by reaction at the secondary hydroxyl group using an activated acid derivative, such as an acid halide O(C(O)B2R9b)2 or an acid halide R9bB2COHal, where B2 and R9b are as defined above and Hal is halogen. The intermediates and final products may be purified, as necessary using column chromatography. Optionally, protecting group strategy, similar to that outlined above in relation to production of monomers containing a group of formula (IVC) may be employed.
Monomers of formula (II) or (III) containing a group of formula (IVE) may be prepared in an analogous manner to monomers containing groups of formula (IVD) or (IVE).
Monomers of formula (II) or (III) containing a group of formula (VA), (VB) or (VC) may be prepared by direct analogy with methods described for monomers containing groups of formula (IVC), (IVD) and (IVE) respectively.
A.2. Comonomers, for Instance Containing a Hydrophobic, Reactive or Ionic Group
The polymer (A) containing pendant zwitterionic groups preferably comprises residues of a further comonomer containing a hydrophobic, functional or ionic group as well as the residues of the comonomer containing a zwitterionic group. The presence of such addition comonomer residues may modify the properties of the copolymer to improve its compatibility with the polymer (B) in the blends of the invention.
It will be appreciated that in some circumstances it may be desirable to use a combination of different comonomers containing different types of groups. Preferably a comonomer of type a), b) and/or c) as defined below or a combination of such comonomers is used, more preferably only one of comonomer types a), b) and c) is used.
A.2.a. Comonomers Containing an Alkyl, Fluoroalkyl or Siloxane Group
The comonomers containing an alkyl-based group for instance a hydrophobic group, or one which contains for instance a fluoroalkyl or siloxane group, are comonomers containing
a) an alkyl group which group optionally contains one or more etheric oxygen atoms and optionally one or more carbon-carbon double or triple bonds for instance which has 6 or more carbon atoms, or
b) a fluoroalkyl group, preferably of 6 or more carbon atoms, which group optionally contains one or more etheric oxygen atoms and optionally one or more carbon-carbon double or triple bonds, or
c) a siloxane group, containing up to 50 silicon atoms, preferably in a linear chain.
Preferably the alkyl or fluoroalkyl groups contains up to 24 carbon atoms, for instance up to 18 carbon atoms. Preferred comonomers containing an alkyl, fluoroalkyl or siloxane group are those of general formula (VI)
Y1xe2x80x94Qxe2x80x83xe2x80x83(VI)
where Y1 is an ethylenically unsaturated polymerisable group selected from 
where R14 is hydrogen or C1-C4 alkyl,
Axe2x80x2 is xe2x80x94Oxe2x80x94 or xe2x80x94NR15xe2x80x94 where R15 is hydrogen or a C1-C4 alkyl group or R15 is a group Q;
K1 is a group xe2x80x94(CH2)lOC(O)xe2x80x94, xe2x80x94(CH)lC(O)Oxe2x80x94, xe2x80x94(CH2)lOC(O)Oxe2x80x94, xe2x80x94(CH2)lNR16xe2x80x94, xe2x80x94(CH2)lNR16C(O)xe2x80x94, xe2x80x94(CH2)lC(O)NR16xe2x80x94, xe2x80x94(CH2)lNR16C(O)Oxe2x80x94, xe2x80x94(CH2)lOC(O)NR16xe2x80x94, xe2x80x94(CH2)lNR16C(O)NR16xe2x80x94 (in which the groups R16 are the same or different), xe2x80x94(CH2)lOxe2x80x94, xe2x80x94(CH2)lSO3xe2x80x94, a valence bond and l is from 1 to 12 and R16 is hydrogen or a C1-C4 alkyl group; and
Q is (a) a straight or branched alkyl, alkoxyalkyl or (oligo-alkoxy)alkyl chain containing, for instance preferably 6 to 24, carbon atoms unsubstituted or substituted by one or more fluorine atoms and optionally containing one or more carbon-carbon double or triple bonds; or
(b) a siloxane group xe2x80x94(CR16a2)qq (SiR16b2) (OSiR16b2)ppR16b in which each group R16a is the same or different and is hydrogen or alkyl of 1 to 4 carbon atoms or aralkyl, for example benzyl or phenethyl, each group R16 is alkyl of 1 to 4 carbon atoms, qq is from 1 to 6 and pp is from 0 to 49.
Preferred comonomers of formula (VI) bearing a group Q include those of formula (VII) and (VIII): 
wherein:
R14, Axe2x80x2, K1 and Q are as defined in relation to formula (VI).
Preferably in the compounds of formula VII) R14 is hydrogen methyl or ethyl, more preferably methyl so that the compound of formula (VII) is preferably an acrylic acid, methacrylic acid or ethacrylic acid derivative.
In the compounds of formula (VIII) K1 may for instance be a valence bond. Where K1 is a group then preferably l is from 1 to 6, more preferably 1, 2 or 3 and most preferably l is 1. When K1 is a group xe2x80x94(CH2)lNR16xe2x80x94, xe2x80x94(CH2)lOC(O)NR16xe2x80x94, xe2x80x94(CH2)lNR16C(O)Oxe2x80x94, xe2x80x94(CH2)lNR16C(O)xe2x80x94, xe2x80x94(CH2)lC(O)NR16xe2x80x94 or xe2x80x94(CH2)lNR16C(O)NR16xe2x80x94 then R16 is preferably hydrogen, methyl or ethyl, more preferably hydrogen.
In the compounds of formula (VIII), preferably the vinyl group is para to the group xe2x80x94K1xe2x80x94Q.
Preferably Q is an alkyl or fluoroalkyl group optionally containing one or more etheric oxygen atoms and optionally one or more carbon-carbon double or triple bonds. More preferably Q is:
an alkyl group of formula xe2x80x94(CR172)mCR173, wherein the groups xe2x80x94(CR172)xe2x80x94 are the same or different, and in each group xe2x80x94(CR172)xe2x80x94 the groups R17 are the same or different and each group R17 is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl and m is from 5 to 23 if Q contains no fluorine atoms or from 1 to 23, preferably 5 to 23, if Q contains one or more fluorine atoms;
an alkoxyalkyl having 1 to 12 carbon atoms in each alkyl moiety; unsubstituted or substituted by one or more fluorine atoms; or
an (oligo-alkoxyl) alkyl group of formula xe2x80x94[(CR172)nO]o (CR182)nR18 where the groups xe2x80x94(CR182)xe2x80x94 are the same or different and in each group xe2x80x94(CR182)xe2x80x94 the groups R18 are the same or different and each group R18 is hydrogen, fluorine or C1-4 alkyl or fluoroalkyl and n is from 2 to 6, preferably 3 to 4, and o is from 1 to 12.
Alternatively, Q may be a group in which one or more of the alkyl or alkylene moieties in such an alkyl, alkoxyalkyl or (oligoalkoxy) alkyl group is replaced by a corresponding alkenyl, alkynyl, alkenylene or alkynylene moiety.
Preferred groups Q include alkyl, alkoxyalkyl and (oligo-alkoxy)alkyl groups optionally containing one or more carbon-carbon double or triple bonds of 8 or more, more preferably 10 or more, even more preferably 12 or more, for instance 14 or more, such as 16 or more carbon atoms. Such groups may contain one or more fluorine atoms and be therefore fluoroalkyl derivatives. Preferably however, such groups do not contain any fluorine atoms.
Particularly preferred groups are straight chain alkyl or fluoroalkyl groups optionally containing one or more carbon-carbon double or triple bonds.
Where Q is a siloxane group, each group xe2x80x94(CR16a2)xe2x80x94 may be the same or different, preferably the same, and preferably each group R16a is hydrogen. Preferably qq is from 2 to 4, and is most preferably 3. Each group xe2x80x94(SiR16b2)xe2x80x94 may be the same or different, preferably the same, and preferably each group R16b is methyl. Preferably pp is from 4 to 29. Preferred comonomers where Q is a siloxane group are those of formula (VII).
In one specific embodiment the group Q does not contain any ethylenic unsaturation, i.e. any carbon-carbon double or triple bonds.
Particular examples of comonomers containing an alkyl, fluoroalkyl or siloxane group include: methylmethacrylate, butylmethacrylate, n-dodecyl methacrylate, octadecyl methacrylate, hexadecyl methacrylate, 1H,1H,2H,2H-heptadecafluorodecyl methacrylate, p-octyl styrene, p-dodecyl styrene and monomethacryloxypropyl terminated siloxanes n-Dodecyl methacrylate is particularly preferred.
Comonomers containing an alkyl or fluoroalkyl, which does not contain a carbon-carbon double or triple, bond, or a siloxane group such as those of formulae (VII) and (VIII) are commercially available or may be prepared by conventional techniques using known reactions.
In a second specific embodiment of such comonomers, the group Q does contain ethylene unsaturation, i.e. one or more carbon-carbon double or triple bonds. Such comonomers may for example contain a vinylic, divinylic, acetylenic or diacetylenic moiety. Comonomers containing acetylenic rather than vinylic unsaturation are in general preferred, especially those containing a single acetylenic group.
Comonomers which contain such an ethylenic unsaturated group, which does not react in the initial polymerisation reaction but which can be subsequently activated, are capable of providing crosslinking between linear polymer chains once the polymer is blended with a polymer (B). Such crosslinking through reaction of ethylenic or acetylenic pendant groups of the polymer A with other groups on polymer A molecules or on polymer B molecules may improve the stability of the blend and is typically formed by irradiation, for example with UV- or gamma-radiation. The crosslinking of such groups may be employed either alone or in addition to the use of a comonomer containing a reactive group as a crosslinkable comonomer as described below.
Particularly preferred crosslinkable comonomers containing a hydrophobic group are those of formula (VIIA) and (VIIIA). 
in which R14, Axe2x80x2 and K1 are as hereinbefore defined and QQ is an alkynyl group containing 6 or more carbon atoms and one or two, preferably one, carbon-carbon triple bonds provided that the acetylenic moieties are not directly bonded to Axe2x80x2 or K1.
Amongst such comonomers it is preferred that QQ is a group containing from 6 to 24 carbon atoms., preferably 8 or more, more preferably 10 or more, even more preferably 12 or more, for instance 14 or more, such as 16 or more carbon atoms.
It is also preferred that the group QQ does not contain a terminal acetylenic moiety, i.e. a group xe2x80x94Cxe2x95x90CH.
A particularly preferred group QQ is 7-dodecynyl and a specific example of a compound of formula (VIIA) containing such a group is dodec-7-ynyl methacrylate.
The compounds of formula (VIIA) and (VIIIA) and other comonomers of formula (VII) and (VIII) containing an ethylenically unsaturated physisorbable group Q, may be prepared by analogy with known methods. Their preparation is illustrated by Reference Example 5.
A.2. (b) Comonomers bearing a reactive group
Preferred comonomers, which contain a reactive functional group capable of providing crosslinking within the polymer (A) or to the polymer (B) and/or providing reactive groups on the surface of the blend of the invention are of general formula (IX)
Y2Q1xe2x80x83xe2x80x83(IX)
where Y2 is an ethylenically unsaturated polymerisable group selected from 
where R19 is hydrogen or C1-C1-C4 alkyl,
K2 is a group xe2x80x94(CH2)qOC(O)xe2x80x94, xe2x80x94(CH)qC(O)Oxe2x80x94, xe2x80x94(CH2)qOC(O)Oxe2x80x94, (CH2)qNR20xe2x80x94, xe2x80x94(CH2)qNR20C(O)xe2x80x94, xe2x80x94(CH2)qC(O)NR20xe2x80x94, xe2x80x94(CH2)qNR20C(O)Oxe2x80x94, (CH2)qOC(O)NR20xe2x80x94, xe2x80x94(CH2)qNR20C(O)NR20xe2x80x94 (in which the groups R20 are the same or different), xe2x80x94(CH2)qOxe2x80x94, or xe2x80x94(CH2)qSO3xe2x80x94, or a valence bond and q is from 1 to 12 and R20 is hydrogen or a C1-C4 alkyl group; and
Q1 is a reactive group capable of reacting to provide crosslinking within the polymer (A) or to the polymer (B) and/or providing a reactive group on the surface of the blend.
Preferred comonomers of formula (IX) bearing a reactive group Q1 include those of formula (X) and (XI) defined below.
The compounds of formula (X) are: 
wherein:
R19 is as defined with reference to formula (X), and.
Q2 is a reactive group.
Preferably in the compounds of formula (X) R19 is hydrogen, methyl or ethyl, more preferably methyl, so that the compound of formula (X) is preferably an acrylic acid, methacrylic acid or ethacrylic acid derivative.
Preferably Q2 is hydrogen, or more preferably xe2x80x94OH or a group of the formula:
xe2x80x94Txe2x80x94B7xe2x80x94Q3
where T is xe2x80x94Oxe2x80x94, or xe2x80x94NR21xe2x80x94 where R21 is hydrogen, C1-C4 alkyl or a group xe2x80x94B7xe2x80x94Q3;
B7 is a valence bond or, more preferably, a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene chain; and
Q3 is a reactive group such as an aldehyde group or a silane or siloxane group containing one or more reactive substituents such- as halogen, for example chlorine, or alkoxy, generally containing from 1 to 4 carbon atoms, for example methoxy or ethoxy, or, more preferably Q3 is a hydroxyl, amino, carboxyl, epoxy, xe2x80x94CHOHCH2Hal, (in which Hal is a halogen atom such as chlorine, bromine or iodine) succinimido, sulphonic acid esters such as tosylate and triflate, imidazole carbonyl-amino, or an optionally substituted triazine group.
Preferably B7 is:
an alkylene group of formula xe2x80x94(CR222)rxe2x80x94, wherein the groups xe2x80x94(CR222)xe2x80x94 are the same or different, and in each group xe2x80x94(CR222)xe2x80x94 the groups R22 are the same or different and each group R22 is hydrogen or C1-4 alkyl, preferably hydrogen, and r is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR232)sO]t(CR232)sxe2x80x94 where the groups xe2x80x94(CR232)xe2x80x94 are the same or different and in each group xe2x80x94(CR232)xe2x80x94 the groups R23 are the same or different and each group R23 is hydrogen or C1-4 alkyl, preferably hydrogen, and s is from 1 to 6, preferably 2 or 3, and t is from 1 to 11, preferably 1 to 5.
Preferred groups B7 include alkylene, oxaalkylene and oligo-oxaalkylene groups of up to 12 carbon atoms.
Where Q3 is a silane or siloxy group, preferably B7 is an alkylene group of 1 to 6, preferably 2 to 4, more preferably 3 carbon atoms.
Particular examples of the group B7 are xe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94 and xe2x80x94(CH2)6xe2x80x94.
The compounds of formula (XI) are: 
wherein K2 is as defined in relation to formula (IX) and;
B8 is a straight of branched alkylene, oxaalkylene or oligo-oxaalkylene chain and
Q4 is a reactive group, for example an aldehyde group or a silane or siloxane group containing one or more reactive substituents such as halogen, for example chlorine, or alkoxy, generally containing from 1 to 4 carbon atoms, for example methoxy or ethoxy, or, more preferably, Q4 is a hydroxyl, amino, carboxyl, epoxy, xe2x80x94CHOHCH2Hal, (in which Hal is a halogen atom such as chlorine, bromine or iodine) succinimido, tosylate, triflate, imidazole carbonyl-amino or optionally substituted triazine group.
In the compounds of formula (XI) preferably the vinyl group is para to the group xe2x80x94K2xe2x80x94B8xe2x80x94Q4.
K2 may for instance be a valence bond. Where K2 is a group then preferably q is from 1 to 6, more preferably 1,2 or 3 and most preferably q is 1. When K2 is a group xe2x80x94(CH2)qNR20xe2x80x94, xe2x80x94(CH2)qOC(O)NR20xe2x80x94, xe2x80x94(CH2)qNR20C(O)Oxe2x80x94, xe2x80x94(CH2)qNR20C(O)xe2x80x94, xe2x80x94(CH2)qC(O)NR20xe2x80x94 or xe2x80x94(CH2)qNR20C(O)NR20xe2x80x94 then R20 is preferably hydrogen, methyl or ethyl, more preferably hydrogen.
Preferably B8 is:
an alkylene group of formula xe2x80x94(CR242)uxe2x80x94, wherein the groups xe2x80x94(CR242)xe2x80x94 are the same or different, and in each group xe2x80x94(CR242)xe2x80x94 the groups R24 are the same of different and each group R24 is hydrogen or C1-4 alkyl, preferably hydrogen, and u is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR252)vO]w(CR25)vxe2x80x94 where the groups xe2x80x94(CR252)xe2x80x94 are the same or different and in each group xe2x80x94(CR252)xe2x80x94 the groups R25 are the same or different and each group R25 is hydrogen or C1-4 alkyl, preferably hydrogen, and v is from 1 to 6, preferably 2 or 3, and w is from 1 to 12, preferably 1 to 6.
Preferred groups B include alkylene, oxaalkylene and oligo-oxaalkylene groups of up to 12 carbon atoms. In one embodiment B8 and K2 contain together up to 12 carbon atoms.
Particular examples of comonomers bearing a reactive group include chloromethylstyrene, methacrylic acid, 2-aminoethylmethacrylate, 2,3-epoxypropyl methacrylate, 3-chloro-2-hydroxypropylmethacrylate, 2-methacryloyloxyethyl-dichloro-1,3,5-triazine, 3-chloro-2-hydroxy-propylmethacrylamide and glycidyl methacrylate and reactive methacrylate esters containing the group HetC(O)Oxe2x80x94 in which (Het) is a heterocyclic ring, for example benzotriazole or imidazole and reactive methacrylate esters containing a group R16OC(O)xe2x80x94 in which R16 is a succinimido or pentafluorophenyl group.
Particularly preferred comonomers bearing reactive groups are 2-aminoethyl-methacrylate and 3-chloro-2-hydroxypropylmethacrylate.
Comonomers bearing a reactive group such as those of formula (X) or (XI), are commercially available or may be prepared by conventional techniques using known reactions.
Comonomers of formula (X), which are dichlorotriazine monomers may be prepared in known manner for example by reacting a substituted hydroxy-alkyl(alk)acrylate or aminoalkyl(alk)acrylate with trichlorotriazine in a suitable solvent and in the presence of a base.
Comonomers of formula (XI) which are reactive methacrylate esters in which the ester groups contains an imidazole group may be prepared in known manner by reacting a substituted hydroxyalkyl(alk)acrylate (e.g. 2-hydroxyethyl-(meth)acrylate), polyethylene-oxide (meth) acrylate or polypropyleneoxide (meth) acrylate with 1,1-carbonyl-diimidazole in a dry solvent. Analogous known methods may be used to prepare succinimido and pentafluorophenyl methacrylate esters of formula (X), by reaction with a reactive ester, acid halide or acid anhydride.
Reactive groups may provide points for the attachment of moieties such as ligands to the surface of the polymer blend.
Comonomers containing a reactive group, such as A compounds of formula (X) and (XI) may also be used as comonomers containing crosslinkable groups (i.e. coreactive groups), which react with other crosslinkable groups (or coreactive groups), either in the polymer (A) or the polymer (B).
Where comonomers containing a reactive group are used to provide such crosslinkable groups then the crosslinkable groups and/or the copolymerisation conditions will be chosen so that they will not crosslink when the comonomers are copolymerised; thus the polymerisation product will be an uncrosslinked linear copolymer which may be subsequently crosslinked after blending the copolymer with polymer (B) so as to improve the stability of the blend. When such crosslinking between linear polymer chains is employed the crosslinkage may be formed either between two such crosslinkable groups or between a crosslinkable group and a non-inert group mutually coreactive in a diluent comonomer residue (defined later). Such a crosslinkage may be formed either by direct reaction of the groups forming the crosslinkage or by reaction of these groups with a reactive bridging molecule for example a reactive gas, such as ammonia.
Residues of such comonomers may therefore be present in polymers which also contain residues of comonomers containing a hydrophobic group such as those of formula (VA), (VB) or (VC) or a comonomer containing an alkyl, fluoroalkyl or siloxane group, which is of formula (VII) or (VIII). Similarly residues of such comonomers may also be present in copolymers which contains residues of a compound containing an ionic group of formula (XIII) or (XIV) as defined below.
Preferred reactive comonomers which are used to crosslink the comonomer, are those of formula (X) or (XI) in which Q2, or Q4 contains a crosslinkable cinnamyl, epoxy, xe2x80x94CHOHCH2Hal (in which Hal is a halogen atom), methylol, silyl, an ethylenically unsaturated crosslinkable group, such as an acetylenic, diacetylenic, vinylic or divinylic group, or an acetoacetoxy or chloroalkyl sulfone, preferably chloroethyl sulphone, group.
Particular examples of comonomers bearing a group capable of crosslinking include methacrolein, cinnamyl methacrylate, 2,3-epoxypropyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, hydroxymethyl methacrylamide, 3-(trimethoxysilyl)propyl methacrylate, 2-acetoacetoxyethyl methacrylate, 3-(vinylbenzyl)-2-chloroethyl sulfone.
When a polymer (A) containing crosslinkable groups, is blended with a polymer (B) the polymer (A) is preferably in substantially uncrosslinked form. After blending and optionally after additional processing steps, crosslinking of crosslinkable groups may be performed to increase the strength and stability of the blend. Such crosslinking may for example be performed upon the final processed and shaped blend.
A.2. (c) Comonomers bearing an ionic group
Comonomers containing an ionic group may serve to improve the miscibility of the polymer (A) with the polymer (B), particularly if polymer (B) itself bears ionically charged groups.
Preferred comonomers bearing an ionic group art of general formula (XII)
Y2xe2x80x94B9xe2x80x94Q5xe2x80x83xe2x80x83(XII)
where Y2 is an ethylenically unsaturated polymerisable group selected from 
where R26 is hydrogen or C1-C4 alkyl;
Axe2x80x3 is xe2x80x94Oxe2x80x94 or xe2x80x94NR27xe2x80x94, wherein R27 is hydrogen or a C1-C4 alkyl group or R27 is a group xe2x80x94B9xe2x80x94Q5;
B9 is a valence bond, a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene group;
K3 is a group xe2x80x94(CH2)xOC(O)xe2x80x94, xe2x80x94(CH)xC(O)Oxe2x80x94, xe2x80x94(CH2)xOC(O)Oxe2x80x94, xe2x80x94(CH2)xNR28xe2x80x94, xe2x80x94(CH2)xNR28C(O)xe2x80x94, xe2x80x94(CH2)xC(O)NR28xe2x80x94, xe2x80x94(CH2)xNR28C(O)Oxe2x80x94, xe2x80x94(CH2)xOC(O)NR28xe2x80x94, xe2x80x94(CH2)xNR28C(O)NR28xe2x80x94 (in which the groups R28 are the same or different), xe2x80x94(CH2)xOxe2x80x94, xe2x80x94(CH2)xSO3xe2x80x94, a valence bond (optionally in combination with B9) and x is from 1 to 12 and R28 is hydrogen or a C1-C4 alkyl group;
Q5 is an ionic group.
Preferred comonomers of formula (XII) are therefore those of formula (XIII) and (XIV); 
wherein:
R26, Axe2x80x3, B9, K3 and Q5 are as defined in relation to formula (XII).
Preferably in the compounds of formula (XIII) R26 is hydrogen, methyl or ethyl, more preferably methyl, so that the compound of formula (XIII) is preferably an acrylic acid, methacrylic acid or ethacrylic acid derivative.
In the compounds of formula (XIV), K3 may for instance be a valence bond. Where K3 is a group then x is preferably from 1 to 6, more preferably 1, 2 or 3 and most preferably x is 1. When k3 is a group xe2x80x94(CH2)xNR26xe2x80x94, xe2x80x94(CH2)xOC(O)NR26xe2x80x94, xe2x80x94(CH2)xNR26C(O)Oxe2x80x94, xe2x80x94(CH2)xNR26C(O)xe2x80x94, xe2x80x94(CH2)xC(O)NR26xe2x80x94 or xe2x80x94(CH2)xNR26C(O)NR26xe2x80x94 then R26 is preferably hydrogen, methyl or ethyl, more preferably hydrogen.
In the compounds of formula (XIV) preferably the vinyl group is para to the group xe2x80x94K3xe2x80x94B8xe2x80x94Q4.
Preferably B9 is:
an alkylene group of formula xe2x80x94(CR292)yxe2x80x94, wherein the groups xe2x80x94(CR292)xe2x80x94 are the same or different, and in each group xe2x80x94(CR292)xe2x80x94 the groups R29 are the same or different and each group R29 is hydrogen or C1-4 alkyl, preferably hydrogen, and y is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety; or
an oligo-oxaalkylene group of formula xe2x80x94[(CR302)yyO]xx (CR302)yyxe2x80x94 where the groups xe2x80x94(CR302)xe2x80x94 are the same or different and in each group xe2x80x94(CR302)xe2x80x94 the groups R30 are the same or different and each group R30 is hydrogen or C1-4 alkyl, preferably hydrogen, and yy is from 1 to 6, preferably 2 or 3, and xx is from 1 to 12, preferably 1 to 6.
Preferred groups B9 include alkylene, oxaalkylene and oligo-oxaalkylene groups of up to 12 carbon atoms.
Particular examples of the group B9 are xe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94 and xe2x80x94(CH2)6xe2x80x94.
The group Q5 may be either anionic or cationic. Where the group Q5 is anionic it may for example be a carboxylate, sulphonate, hydrogenphosphate or phosphate group. Where the group Q5 is cationic it may for example be a group xe2x80x94N.R313 in which each group R31 is the same or different, and is hydrogen or alkyl of 1 to 6 carbon atoms two of which groups R31 may together from a heterocyclic ring containing from 5 to 7 atoms, preferably hydrogen or methyl, a group N.Het, where Het is an unsaturated heterocyclic group such as pyridyl, substituted or unsubstituted by one or more alkyl groups of 1 to 4 carbon atoms, or a group xe2x80x94P.R323 in which each group R32 is the same or different and is hydrogen or alkyl of 1 to 6 carbons atoms, two of which groups R31 may together form a heterocyclic ring containing from 5 to 7 atoms, preferably methyl.
Particular examples of comonomers bearing an ionic group include acrylic acid, methacrylic acid, 2-sulfoethyl methacrylate, 2-methacryloyloxyethyl phosphate, p-styrene sulfonic acid, 2-(methacryloyloxyethyl)trimethylammonium chloride, 3-aminopropyl methacrylamide and vinylbenzyl trimethylammonium chloride.
Comonomers containing an ionic group such as those of formula (XIII) and (XIV) are commercially available or may be prepared by conventional techniques using known reactions.
A.3. Diluent Comonomers
In addition to A.1. the residues of monomers containing a zwitterionic, and optionally A.2. residues of comonomers containing an alkyl (optionally substituted) hydrophobic group, reactive functional group or ionic group, the polymers (A) bearing pendant zwitterionic groups may comprise residues of a diluent comonomer.
Such diluent comonomers may be used to give the polymer physical and mechanical properties desirable for blending with the polymer (B) for example to improve miscibility. They may be of any known conventional radical polymerisable, preferably ethylenically unsaturated, type compatible with other comonomer(s).
Particular examples of diluent comonomers include alkyl(alk)acrylate preferably containing 1 to 4 carbon atoms in the alkyl group of the ester moiety, such as methyl (alk)acrylate; a mono- or, usually di-alkylamino alkyl(alk)acrylate, preferably containing 1 to 4 carbon atoms in the or each alkyl moiety of the amine and 1 to 4 carbon atoms in the alkylene chain, e.g. 2-(dimethylamino)ethyl (alk) acrylate; and (alk)acrylamide, such as acrylamide; an alkyl- or dialkyl- (alk)acrylamide preferably containing 1 to 4 carbon atoms in the alkyl group of the amide moiety; a hydroxyalkyl (alk)acrylate preferably containing from 1 to 4 carbon atoms in the hydroxyalkyl moiety, e.g. a 2-hydroxyethyl (alk)acrylate; a vinyl monomer such as an N-vinyl lactam, preferably containing from 5 to 7 atoms in the lactam ring, for instance vinyl pyrrolidone, or an ester such as vinyl acetate; or styrene or a styrene derivative which for example is substituted on the phenyl ring by one or more alkyl groups containing from 1 to 6, preferably 1 to 4, carbon atoms, and/or by one or more halogen, such as fluorine atoms, e.g. (pentafluorophenyl)styrene.
Other suitable diluent comonomers include polyhydroxyl, for example sugar, (alk)acrylates and (alk)acrylamides in which the alkyl group contains from 1 to 4 carbon atoms, e.g. sugar acrylates, -methacrylates, -ethacrylates, -acrylamides, -methacrylamides and -ethacrylamides. Suitable sugars include glucose and sorbitol. Particularly suitable diluent comonomers include methacryloyl glucose or sorbitol methacrylate.
Further diluents which may be mentioned specifically include polymerisable alkenes, preferably of 2-4 carbon atoms, eg. ethylene, dienes such as butadiene, alkylene anhydrides such as maleic anhydride and cyano-substituted alkylenes, such as acrylonitrile.
Diluent comonomers may be obtained by conventional known methods.
Of the above diluent comonomers some are inert and act simply to modify the physical and mechanical properties of copolymers containing them. Others, and in particular the hydroxyalkyl(alk)acrylates and polyhydroxyl (alk)acrylates have a reactive role in addition to simply modifying physical and mechanical properties. Such comonomers contain functional groups, such as hydroxyl groups, which may react with a crosslinking group or may react with reactive groups in other molecules to attach them to the copolymer.
Preparation of Polymer (A)
The polymers (A) bearing pendant zwitterionic groups formed from polymerisable ethylenically unsaturated groups may be prepared by conventional techniques for polymerisation, typically thermal or photochemical polymerisation. Where comonomers capable of producing crosslinking are present, the polymerisation conditions are set such that crosslinking does not occur during polymerisation. Thus, for example, actinic radiation would not be used to prepare a polymer containing a monomer which can form crosslinks by exposure to actinic radiation.
For thermal polymerisation a temperature from 40 to 100xc2x0 C., typically 50 to 80xc2x0 C. is used. For photochemical polymerisation actinic radiation such as gamma, U.V., visible, or microwave radiation may be used. Typically U.V. radiation of wavelength 200 to 400 nm is used.
The polymerisation is generally performed in a reaction medium, which is for instance a solution or dispersion using as a solvent for example acetonitrile, dimethyl formamide, chloroform, dichloromethane, ethyl acetate, dimethyl sulphoxide, dioxan, benzene, toluene, tetrahydrofuran, or where the polymer does not contain groups which react with protic solvents, water or an alkanol containing from 1 to 4 carbon atoms, e.g. methanol, ethanol or propan-2-ol. Alternatively, a mixture of any of the above solvents may be used.
The polymerisation may be carried out in the presence of one or more polymerisation initiators, usually free radical generators, usually peroxides or azo initiators, such as benzoyl peroxide, 2,2xe2x80x2-azo-bis(2-methylpropionitrile) or benzoin methyl ether. Other polymerisation initiators which may be used are disclosed inxe2x80x9cPolymer Handbookxe2x80x9d, 3rd edition, Ed. J. Brandrup and E. H. Immergut, Pub. Wiley-Interscience, New York, 1989.
Generally the polymerisation is performed for 1 to 72 hours, preferably 8 to 48, for instance 16 to 24 hours, and under an inert atmosphere of for example nitrogen or argon. The polymer is generally purified by dialysis, precipitation in a non-solvent (e.g. diethyl ether or acetone) or ultrafiltration. The resulting polymer is generally dried under vacuum, eg. for 5 to 72 hours and has a molecular weight from 10,000 to 10 million, preferably from 20,000 to 1 million.
The precise proportion and nature of the various comonomers used to prepare a copolymer comprising residues of a comonomer containing a zwitterionic group and a further comonomer may be adjusted to provide a copolymer which is particularly suitable for blending to a particular polymer (B). The monomer composition which is subjected to polymerisation to provide a polymer according to the invention comprises a minimum of 0.01%, preferably 1%, more preferably 5% by weight of monomer or monomers containing a zwitterionic group bearing a centre of permanent positive charge and a maximum of 99.9%, preferably 99%, more preferably 95% by weight of other monomer or monomers. Such other monomer or monomers may be a monomer or monomers containing an optionally substituted alkyl (usually hydrophobic) group, a reactive functional group, an ionic group or a diluent monomer or monomers.
Where the polymer (A) is a copolymer comprising residues of comonomer bearing zwitterionic groups and comonomer containing an optionally substituted alkyl group then preferably the comonomer composition comprises no more than 95%, more preferably no more than 90% and even more preferably no more than 80% by weight of comonomer or comonomers containing an alkyl group (eg hydrophobic alkyl, fluoroalkyl or siloxane group) the balance of the composition being comonomer or comonomers containing a zwitterionic group diluent monomer or monomers and/or crosslinkable monomer or monomers (i.e. which cross-link during the polymerisation reaction). Such a composition typically comprises up to 50% by weight of diluent comonomer or comonomers. Where diluent comonomer is present, it preferably comprises at least 1%, more preferably 5%, by weight of the total comonomer composition. Where present, crosslinkable comonomer or comonomers generally comprise from 0.1% to 20% by weight of the total comonomer composition.
Preferably the molar ratio such a copolymer of comonomer residues bearing a zwitterionic group to comonomer residues containing a hydrophobic alkyl, fluoroalkyl or siloxane group is from 5:95 to 80:20, more preferably 10:90 to 50:50. In addition the copolymer preferably comprises from 5% to 50%, more preferably 10% to 25%, by mole residues of diluent monomer and/or from 0.1 to 20%, more preferably 1% to 10%, by mole residues of crosslinkable comonomer, provided that where residues of both diluent and crosslinkable comonomer are present, they do not exceed in combination 50%, preferably 35% by mole.
Where the polymer (A) is a copolymer comprising residues of a comonomer which comprises a reactive group or ionic group, preferably the molar ratio of residues of bearing a zwitterionic group to residues containing a reactive group or ionic group is from 10:90 to 95:5, more preferably 50:50 to 90:10. In addition the copolymer preferably comprises from 5% to 50%, more preferably 10% to 25%, by mole residues of diluent monomer and/or from 0.1 to 20%, more preferably 1% to 10%, by mole residues of crosslinkable comonomer, provided that where residues of both diluent and crosslinkable comonomer are present, they do not exceed in combination 50%, preferably 35% by mole.
In addition the monomer or comonomer composition may comprise further components such as a polymerisation initiator, chain transfer agent, acid, base, surfactant, emulsifier or catalyst of conventional type each in an amount from 0.1% to 5%, typically from 0.2% to 3% and preferably about 0.5%, by weight each relative to the total weight of the monomers.
According to the present invention, the polymer (A) containing pendant zwitterionic groups is blended with a polymer (B) having desirable physical and/or mechanical properties. Such a polymer may be a thermoplastic, elastomer or thermosetting material. Preferably, the polymer (B) is a thermoplastic such as a polyolefin, polyvinylchloride (PVC), poly(alk)acrylate, such as methyl methacrylate, polyurethane, or fluorinated polyolefin.
In particular, the polymer (B) may be a polymer or copolymer, or a mixture of polymers or copolymers, which is already known for use in a particular application, such as a biomedical application. Table 1 below lists known polymers with biomedical applications which may be used in the blends of the present invention:
Generally the blends of the present invention will contain from 1 to 90% by weight of polymer (A) containing pendant zwitterionic groups and from 99 to 10% of polymer (B) having desirable physical and/or mechanical properties. The precise proportions of the polymers (A) and (B) will depend upon the compatibility of the two polymers for blending and, it may be necessary to test the polymers together for their compatibility. This may be achieved by blending different proportions of the polymers (A) and (B) to obtain a blend with the desired balance of mechanical and physical properties as well as biocompatibility. In particular, the proportions of the two polymers may be adjusted so as to obtain desired impact resistance, tensile strength, flexural modulus, low temperature brittleness, friction co-efficient, film permeability, film tear resistance, film shrinkage, surface and volume resistivity, surface wettability and/or contact angle.
The minimum quantity of polymer (A) will depend upon the particular polymer (B), the content of zwitterionic groups in the polymer (A) and the desired use of the blend. However, the content of polymer (A) should be sufficient to provide a detectable modification to the biocompatible properties of the blend compared to the unblended polymer (B). Preferably the blend will contain at least 1%, more preferably 10% and still more preferably 30% of polymer (A). The improvement in each of the fibrinogen absorption and the platelet activation should be so as to achieve a value of less than 80%, more preferably less than 60% of the value of polymer B alone.
It is believed the improved biocompatibility is due in part to increased hydrophilicity compared to the base polymer. Another property which improves and which may also be due in part to increased hydrophilicity is lubricity i.e. a reduced co-efficient of friction. The improved wettability due to increased hydrophilicity (which can be observed by determining the contact angle of water on the surface) may allow water to act as a wetting lubricant to a greater extent due to the zwitterionic groups. This may be a desirable property, for instance where a product is required to slide easily in contact with other surfaces, eg within the body, minimal modification to the biocompatible properties may be tolerated in the invention if accompanied by increased lubricity especially where a product is in contact with the body for a short time only, eg catheters and the like.
This increased lubricity forms the basis for a further invention in which the coefficient of friction in the presence of aqueous liquid of the surface of an article is reduced by the provision of bound zwitterionic groups.
In this invention the zwitterionic groups may be any of those defined by group X above. The zwitterionic group, is bound at the surface such that it is not removed by aqueous liquid in contact with the surface and so is usually covalently bound to polymer which forms the surface or is on the surface and which is water-insoluble. In some circumstances it may be possible for the zwitterionic group to be a part of a polymer which is itself water-soluble but is bound to a substrate surface so that it cannot be removed by water e.g. by being bound by strong ionic bonds or by hydrogen-bonding interaction.
In the preferred embodiment of the invention the zwitterionic groups are introduced at the surface of the article as pendant groups on a polymer A which is blended with a polymer B having suitable physical and/or mechanical properties and the blend of the polymers is then used to form the article, for instance by shaping as described above. However it is alternatively possible to introduce the zwitterrionic groups by coating a polymer containing such groups on to the surface of a preformed article. The polymer may, after coating, be bound to the article by hydrogen-bonding interactions, by chemical reaction to provide a covalent bond with the underlying polymer surface or by counterionic attraction between oppositely charged ionic groups on the coating polymer and on the coated surface. Products of this type are described in our earlier application (not published at the priority date of the first invention herein) WO-A-9301221.
Other ways of providing articles having zwitterionic groups at the surface where the article is formed of a reactive, usually polymeric material are by chemical reaction of a preformed article with a reagent which comprises the zwitterionic group and a chemically reactive group which is suitable for reaction with the material at the surface. Various derivatisation reactions of this type are described in our earlier applications EP-A-0032622, EP-A-0157469, WO-A-9113639 and WO-A-9305081. A further way of incorporating the zwitterionic group is to form a polmer from monomers including at least one monomer which has a zwitterionic group. Such monomers may be for formation of polyesters, for instance as described in our earlier publication EP-A-0275293, for formation of polyurethanes, for instance as described in EP-A-0199790, or for formation of addition polymers from ethylenically unsaturated monomers for instance as described in WO-A-9207885.
The utility of this invention is primarily in the medical field,for instance for any instrument which is. required to slide against any other surface in the presence of aqueous liquid, usually body fluids. Such instruments are for instance catheters, guide wires, endoscopes, instruments used in keyhole surgery, ostomy connectors or other permanent ports, dilators of various types, contact lenses, etc. The increased lubricity can be demonstrated qualitatively by observing the slipperiness of the article in the presence of water or other aqueous liquid. The coefficient of friction measured by routine techniques can be used to give a quantitative measurement of the increased lubricity, for instance as compared to the article formed in the absence of the zwitterionic groups or polymer containing the zwitterionic groups.
In addition, the blends of the present invention may further comprise conventional additives used in polymeric materials such as plasticisers, fillers, colourants, UV absorbers, anti-oxidants and/or preservatives, such as biocides, which may be included in conventional amounts so as to be compatible with the polymers present in the blend.
The present invention further provides a process for producing a blend of the present invention, which comprises blending a preformed polymer (A) bearing zwitterionic pendant groups and a polymer (B) having desirable mechanical and/or physical properties.
Such blending may be carried out by conventional techniques for blending solid or liquid polymeric materials, including known solid state physical mixing techniques such as roll-milling, Banbury mixing, screw extrusion and disk compounding. Alternatively, blending may be carried out using aqueous dispersions and/or solutions of the polymers (A) and (B) or dispersions and/or solutions of the polymers (A) and (B) in an organic solvent and the water and/or solvent removed for instance by evaporation or by precipitation of polymer followed by liquid/solid separation as normal. Such blending may be carried out using conventional liquid phase blending techniques such as high or low shear mixers. These techniques are used as for known polymer blending operations. Using routine procedures suitable mixing conditions and choice of ingredients can be selected to obtain a blend having the desired homogeneity. Crosslinking or other chemical reacion may take place during mixing, as is known in the blending art.
Where the polymer (B) is a thermoset polymer, blending by such mixing techniques may not be possible. In such circumstances, it may therefore be necessary to include the polymer (A) in a blend with the monomers of the polymer (B) or a pre-polymer of polymer (B) prior to final polymer formation eg cross-linking to form the thermoset material. Clearly, in such circumstances, polymer (A) must be able to withstand the polymerisation conditions and/or cross-linking conditions for polymer (B) without adverse effects. Where the polymer (A) also includes reactive or cross-linkable groups, then these may take part in the thermosetting reaction or crosslink to the polymer (B) to modify the properties of the final blended polymer.
The invention further provides a shaped article formed from a polymeric blend according to the present invention. Such articles may be formed in a conventional manner, for example by extrusion or injection moulding or other moulding techniques and/or by machining as necessary for the desired end shape appropriate to the nature of the particular material in question, for instance for the uses mentioned in table 1 above, in which the surface of the article is in contact with a biological liquid. Usually a protein- or cell-containing liquid, such as blood, plasma, serum or tear film.
In particular, the blends of the present invention are suitable for use in surgical implants or prostheses, bioseparation apparatus, blood carrier bags, dialysis membranes, blood oxygenator films, tubing for use in prostheses, in extra corporeal circuitry or in catheters, connectors, stoppers, closures for diagnostic catheters, surgical drapes and tapes, and encapsulants for bio-medical applications. In addition, they are suitable for use as casings for electronic devices, as contact lenses, intra-ocular lenses and other ophthalmic implants and cell culture materials.
The blends of the present invention are preferred to graft polymers with zwitterionic groups formed according to WO-A-9305081 as they allow for a wider range of base polymers A and B to be used and, since the polymers can be purified to remove unreacted monomer or low molecular weight oligomer before blending with ease, provide products without problems of contamination by low molecular weight impurities.